Polyethylene glycol (“PEG”) is a linear or branched, neutral polyether, available in a variety of molecular weights. The structure of PEG is HO—(CH2—CH2—O)n—H, where n indicates the number of repeats of the ethylene oxide unit in the PEG.
PEG and PEG derivatives have been employed to modify a variety of biomolecules. When attached to such molecules, PEG increases their solubility and increases their size, but has little effect on desirable properties.
Advantageously, PEG conjugated biomolecules may exhibit increased retention and delayed metabolism in the body.
A variety of PEG derivatives has been developed for such applications. Such PEG derivatives are described, for example, in U.S. Pat. Nos. 5,252,714; 5,672,662; 5,959,265; 5,990,237; and 6,340,742.
Two general approaches have been used for the functionalization of PEG: (1) changing the terminal hydroxyl group, through a series of reactions, to a more active functional group and/or (2) reaction of the PEG under controlled conditions with difunctional compounds so that one of its functional groups reacts with the PEG polymer and the other remains active. In most cases, several steps must be conducted to achieve the desired PEG derivatives. The desired PEG derivatives are often produced in low yields and require a complicated purification process to isolate. In addition, PEG derivatives may show nonspecific binding to the biomolecules of interest, which can result in multiple PEGs attached to a single biomolecule and/or PEG attachment at the active site. Multiple PEG attachments may cause difficulty in purification of the pegylated biomolecule. Multiple PEG attachments, and/or pegylation at the active site, can also lead to decreased activity of the biomolecule.
It would, therefore, be advantageous to provide improved PEG derivatives suitable for conjugation with a variety of other molecules, including polypeptides and other biomolecules containing an α-amino group. There remains a need to provide PEG derivatives that can be produced in high yield and purity, and that can be conjugated to provide biomolecules having improved performance characteristics.
These and other objects of the present invention are described in greater detail below.